83 practice questions on Semiconductor Electronics , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Semiconductor Electronics notes .
Conductor conduction band valence band bands overlap Semiconductor conduction band valence band small gap (~1 eV) Insulator conduction band valence band large gap (> 3 eV) Conductors have overlapping bands, semiconductors have a small energy gap that can be bridged by heat or doping, and insulators have a large gap that blocks conduction.
Easy - 24 questions Q1.
The forbidden energy gap between the valence and conduction bands of a good conductor is:
A large, about 6 eVB zero or overlappingC about 1 eVD about 3 eVShow answer & explanation →
Q2.
A transistor works as a linear amplifier when it is biased in its:
A cut-off regionB saturation regionC breakdown regionD active regionShow answer & explanation →
Q3.
Adding a trivalent impurity such as boron to pure silicon produces a:
A n-type semiconductorB p-type semiconductorC intrinsic semiconductorD an insulatorShow answer & explanation →
Q4.
When a p-n junction is reverse biased, the width of the depletion region:
A decreasesB becomes zeroC increasesD stays constantShow answer & explanation →
Q5.
A semiconductor has electrical conductivity:
A Higher than metals in the majority of cases studiedB Lower than insulators as widely reportedC Between metals and insulatorsD Equal to metals in standard practiceShow answer & explanation →
Q6.
N-type semiconductor is doped with:
A Trivalent impurity (e.g., boron)B Pentavalent impurity (e.g., phosphorus)C Both trivalent and pentavalentD No impurityShow answer & explanation →
Q8.
In forward biased p-n junction:
A Depletion region widens, blocking nearly all current flowB No current flows because the barrier potential is unaffectedC Depletion region narrows and current flowsD Only holes move across the junction while electrons stay fixedShow answer & explanation →
Q9.
In a p-n junction diode, current flows easily in:
A Reverse bias onlyB Forward bias onlyC Both directions equallyD Neither directionShow answer & explanation →
Q11.
LED emits light when:
A In reverse bias, where the depletion region widensB Heated externally without any applied bias voltageC In forward bias (electron-hole recombination)D Cooled well below room temperature with no applied voltageShow answer & explanation →
Q12.
NPN transistor has three terminals:
A Emitter, Base, CollectorB Gate, Source, DrainC Anode, Cathode, GridD Source, Sink, ChannelShow answer & explanation →
Q14.
NOT gate produces output that is:
A Identical to the input signal with no changeB Inverted (complement) of inputC The logical AND of two separate input signalsD The logical OR of two separate input signalsShow answer & explanation →
Q17.
Conductivity of semiconductor increases with temperature because:
A Resistance decreases under most conditions encounteredB More electron-hole pairs are createdC Mobility increases mainly as frequently observed in practiceD Charge density decreases in many documented casesShow answer & explanation →
Q18.
Solar cell converts:
A Electrical to light energyB Light to electrical energyC Heat to electrical energyD Mechanical to electrical energyShow answer & explanation →
Q20.
The depletion region in a p-n junction is depleted of:
A Electrons mainly, while holes remain freely mobile thereB Holes mainly, while electrons remain freely mobile thereC Both mobile charge carriers (electrons and holes)D All atoms, leaving a literal physical gap in the crystalShow answer & explanation →
Q21.
OR gate output is 1 when:
A Both inputs are 0B At least one input is 1C Both inputs are 1 onlyD Neither input is 1Show answer & explanation →
Q22.
AND gate output is 1 when:
A At least one input is 1B Only one input is 1C All inputs are 1D Neither input is 1Show answer & explanation →
Q23.
A full-wave rectifier has _____ diodes:
A Just 1 diode, as in a basic half-wave rectifierB 2 diodes, as in a center-tap full-wave rectifierC 3 diodes, an unused odd configurationD 4 (bridge rectifier)Show answer & explanation →
Q24.
Intrinsic semiconductor at absolute zero behaves as:
A Good conductorB Perfect insulatorC SemiconductorD SuperconductorShow answer & explanation →
Medium - 26 questions Q25.
A Zener diode of breakdown voltage 6 V is used in a regulator with a 9 V supply and a 300 Ω series resistor. The current through the series resistor is:
A 10 mAB 5 mAC 20 mAD 30 mAShow answer & explanation →
Q26.
A full-wave rectifier is supplied from a 50 Hz AC mains. The fundamental ripple frequency of its output is:
A 25 HzB 50 HzC 100 HzD 200 HzShow answer & explanation →
Q27.
In a common-emitter transistor, the base current is 20 μA and the collector current is 2 mA. The current gain β is:
Show answer & explanation →
Q29.
The forward characteristic of a diode shows a voltage change of 0.1 V producing a current change of 2 mA. Its dynamic resistance is:
A 50 ΩB 20 ΩC 0.02 ΩD 200 ΩShow answer & explanation →
Q30.
In a common-base transistor, α = 0.95 and the emitter current is 1 mA. The collector current is:
A 1.05 mAB 0.95 mAC 0.05 mAD 1.00 mAShow answer & explanation →
Q33.
In forward-biased p-n junction, the depletion region:
A WidensB Narrows (barrier reduces)C Stays sameD Disappears completelyShow answer & explanation →
Q34.
The Hall effect is used to determine:
A The band gap energy of the semiconductor material according to most researchersB Type of charge carrier (electron or hole) and carrier concentrationC The temperature coefficient of resistivity for the material in the majority of cases studiedD The reverse breakdown voltage of a p-n junction diode as widely reportedShow answer & explanation →
Q35.
The threshold voltage of a MOSFET is the gate voltage at which:
A Significant gate leakage current begins to flow through the oxideB Inversion layer forms (channel becomes conducting)C The drain current becomes equal to the supply currentD The source and drain terminals become directly shorted togetherShow answer & explanation →
Q36.
The breakdown mechanism in heavily doped p-n junctions at low reverse voltage:
A Avalanche breakdown, which dominates instead in lightly doped junctionsB Zener breakdown (quantum tunneling across thin depletion region)C Thermal breakdown caused by excessive self-heating of the junctionD Ohmic breakdown caused by simple resistive heating at high currentShow answer & explanation →
Q38.
The base of a BJT transistor is:
A Very thick with high doping in standard practiceB Very thin with low doping (lightly doped)C Same as emitter under most conditions encounteredD Not connected as frequently observed in practiceShow answer & explanation →
Q39.
Transconductance gm of a MOSFET is:
A dI_D/dV_G (change in drain current per gate voltage)B V<sub>G</sub>/I<sub>D</sub>, the ratio of gate voltage to drain currentC R<sub>channel</sub>, the plain ohmic resistance of the conducting channelD dV_D/dI_G, the rate of change of drain voltage with gate currentShow answer & explanation →
Q40.
In an intrinsic semiconductor, np product =
A n² alone, with little relation to the hole concentrationB ni² where ni is intrinsic carrier concentrationC n+p, the simple sum of electron and hole concentrationsD Zero, as if electrons and holes rarely coexisted in the latticeShow answer & explanation →
Q41.
LED efficiency (quantum efficiency) is limited by:
A The doping concentration alone, with all other factors fixed in many documented casesB Non-radiative recombination, optical extraction losses, and interface defectsC The applied forward voltage alone, independent of material quality according to conventional understandingD The temperature coefficient of resistivity of the semiconductor in routine practiceShow answer & explanation →
Q42.
Ohmic contact between metal and semiconductor requires:
A A lightly doped semiconductor region at the metal interfaceB Formation of a rectifying Schottky barrier at the junctionC Heavily doped semiconductor (tunneling through thin barrier)D An intrinsic, undoped semiconductor region at the contactShow answer & explanation →
Q43.
The CMOS inverter uses:
A Mainly NMOS transistors arranged in a push-pull configurationB Both NMOS and PMOS transistors complementarilyC Mainly PMOS transistors arranged in a push-pull configurationD Bipolar junction transistors instead of field-effect transistorsShow answer & explanation →
Q44.
Fermi level in n-type semiconductor shifts:
A Toward valence bandB Toward conduction bandC Does not shiftD To mid-gap exactlyShow answer & explanation →
Q45.
The built-in potential (contact potential) across a p-n junction:
A Can be measured with voltmeter directly overallB Cannot be utilized as a battery (thermal equilibrium)C Decreases with doping in most cases under typical conditionsD Is zero at room temperature according to standard textbooksShow answer & explanation →
Q46.
Photovoltaic effect in solar cells converts:
A Heat energy directly into electrical energy, in the manner of a thermocouple junctionB Light to electricity (photons creating electron-hole pairs separated by p-n junction field)C Electrical energy back into emitted light, in the manner of a forward-biased LEDD Stored chemical energy directly into electrical energy, in the manner of a batteryShow answer & explanation →
Q47.
Bipolar transistor current gain beta = hFE represents:
A I<sub>B</sub>/I<sub>C</sub>, the reciprocal of the actual current gain ratioB I<sub>C</sub>/I<sub>B</sub> (collector current divided by base current)C I<sub>E</sub>/I<sub>C</sub>, the ratio of emitter current to collector currentD V<sub>CE</sub>/V<sub>BE</sub>, a ratio of voltages rather than currentsShow answer & explanation →
Q48.
Drift current in semiconductor is caused by:
A Concentration gradientB Applied electric fieldC Temperature gradientD Magnetic field onlyShow answer & explanation →
Q49.
The I-V equation of a p-n junction diode (Shockley equation):
A I = I₀(e<sup>V/VT</sup> - 1)B I = V/RC I = I₀ VD I = I₀ e<sup>-V</sup>Show answer & explanation →
Q50.
In which region does MOSFET act as a voltage-controlled resistor?
A Saturation region in general practiceB Subthreshold region as frequently describedC Triode (linear/ohmic) regionD Breakdown region in most textbook accountsShow answer & explanation →
Hard - 33 questions Q51.
In an n-type silicon sample the intrinsic concentration is 1.5 × 10<sup>16</sup> m<sup>-3</sup> and the electron concentration is 5 × 10<sup>22</sup> m<sup>-3</sup>. The hole concentration is:
A 2.25×10<sup>9</sup> m<sup>-3</sup>B 5×10<sup>22</sup> m<sup>-3</sup>C 4.5×10<sup>9</sup> m<sup>-3</sup>D 1.5×10<sup>16</sup> m<sup>-3</sup>Show answer & explanation →
Q52.
An LED emits light of wavelength 620 nm. The band gap of the semiconductor used is about (take hc = 1240 eV·nm):
A 1.1 eVB 1.4 eVC 3.0 eVD 2.0 eVShow answer & explanation →
Q53.
A 10 V Zener diode is connected in reverse across a load through a 1 kΩ series resistor, with a 15 V supply. The current through the series resistor is:
A 5 mAB 10 mAC 15 mAD 2.5 mAShow answer & explanation →
Q54.
A NAND gate followed by a NOT gate behaves overall as which single gate?
A OR gateB AND gateC NOR gateD XOR gateShow answer & explanation →
Q55.
A full-wave rectifier delivers a peak output voltage of 10 V to a resistive load. The average (DC) output voltage is about:
A 3.18 VB 10 VC 6.37 VD 7.07 VShow answer & explanation →
Q56.
The Einstein relation between mobility and diffusion coefficient is:
A D = mu × kT/eB D = mu × e/kTC D = mu × kTD D/mu = eShow answer & explanation →
Q57.
In an npn BJT in active region: I<sub>E</sub> = I<sub>C</sub> + I<sub>B</sub>. The emitter injection efficiency gamma is:
A I<sub>Cn</sub>/I<sub>E</sub>B I<sub>Cp</sub>/I<sub>E</sub>C I<sub>E</sub>/I<sub>C</sub>D I<sub>B</sub>/I<sub>C</sub>Show answer & explanation →
Q58.
Shockley-Read-Hall (SRH) recombination occurs via:
A Direct band-to-band recombinationB Trap levels in mid-gapC Auger processD Phonon emission onlyShow answer & explanation →
Q59.
The channel pinch-off in JFET/MOSFET occurs when:
A V<sub>GS</sub> = 0, with the gate-source voltage held at exactly zeroB V<sub>DS</sub> = V<sub>GS</sub> - V<sub>p</sub> (or V<sub>GS</sub> - Vth)C I<sub>D</sub> = 0, as if the drain current vanished largely at pinch-offD V<sub>GS</sub> > 0, a condition with little relation to the actual pinch-off pointShow answer & explanation →
Q60.
Quantum confinement in semiconductor nanostructures (quantum dots) causes:
A A continuous, bulk-like band structure with little discrete levelsB Discrete energy levels and size-tunable bandgapC Metallic, conductor-like behavior with little bandgapD A bandgap that shrinks to exactly zero regardless of dot sizeShow answer & explanation →
Q61.
The NMOS long-channel drain current in saturation (I<sub>D</sub>,sat) ∝
A (V<sub>GS</sub> - Vth)B (V<sub>GS</sub> - Vth)²C (V<sub>GS</sub> - Vth)<sup>0.5</sup>D V<sub>DS</sub>Show answer & explanation →
Q62.
Generation-recombination current in reverse-biased diode scales as:
A exp(-E<sub>g</sub>/kT), the simple intrinsic-carrier exponential with little factor of twoB exp(-E<sub>g</sub>/2kT) (via mid-gap traps)C ni² × exp(V/2VT), an expression with an incorrect forward-bias-like voltage termD 1/T, a simple inverse-temperature dependence with little exponentialShow answer & explanation →
Q63.
In a CMOS circuit, the power consumption P<sub>dynamic</sub> =
A I × V, the basic instantaneous power formula with no switching-frequency termB C × V² × f (capacitance × supply voltage squared × frequency)C V²/R, the static power dissipation formula for a simple resistorD I² × R, the static power dissipation formula in terms of currentShow answer & explanation →
Q64.
The heterojunction (type I): electrons tend to accumulate in:
A Wider bandgap material, which has a higher conduction band minimumB Narrower bandgap material (lower conduction band minimum)C Whichever side happens to be doped p-type, regardless of bandgapD Whichever side happens to be doped n-type, regardless of bandgapShow answer & explanation →
Q65.
Negative differential resistance (NDR) is observed in:
A Standard ohmic resistors, where resistance never decreases with currentB Tunnel diodes (Esaki diodes) at forward biasC Ideal p-n junction diodes under normal forward or reverse biasD Ordinary Schottky diodes used for fast rectificationShow answer & explanation →
Q66.
The Zener diode breakdown voltage temperature coefficient is:
A Always positive, regardless of the underlying breakdown mechanismB Negative for Zener (<5V), positive for avalanche (>7V)C Exactly zero, with the breakdown voltage independent of temperatureD Independent of mechanism, with Zener and avalanche behaving identicallyShow answer & explanation →
Q67.
The depletion approximation in p-n junction analysis assumes:
A A gradual, smoothly varying doping profile across the junctionB Complete ionization within depletion region and zero carriers (sharp boundary)C A significant population of mobile carriers within the depletion regionD An intrinsic, undoped semiconductor on both sides of the junctionShow answer & explanation →
Q68.
Phonon dispersion in semiconductor: acoustic vs optical modes differ because:
A Acoustic modes involve same-sub-lattice atoms moving in phase; optical involve opposite sublattice atoms out of phaseB Acoustic modes actually exhibit a higher vibrational frequency throughout the Brillouin zone than optical modes doC Optical phonon modes are actually what carry ordinary sound waves through the crystal latticeD Acoustic and optical phonon modes are physically identical in dispersion and frequency in every respectShow answer & explanation →
Q69.
The charge control model of BJT describes:
A Mainly the static DC bias point, with little transient informationB Transient response via stored charge in base (Q<sub>B</sub> = I<sub>C</sub> × tau_F)C Mainly the large-signal switching behavior, ignoring small-signal responseD Random thermal and shot noise generated within the transistorShow answer & explanation →
Q70.
Channel length modulation in MOSFET causes:
A A shift in the threshold voltage of the transistor itselfB Non-zero output conductance (dI_D/dV_DS) in saturationC Complete pinch-off of the channel with zero drain currentD Leakage current flowing directly through the gate oxideShow answer & explanation →
Q71.
In a 2DEG (2D electron gas) at heterojunction, mobility is very high because:
A A higher concentration of dopant atoms is introduced near the channelB Electrons spatially separated from ionized dopants, reducing Coulomb scatteringC The device is simply operated at a lower temperature with no spatial effectD A thicker semiconductor layer is used in the heterostructureShow answer & explanation →
Q72.
The Gunn effect in GaAs: electrons in high electric field undergo:
A Simple velocity saturation, as seen in ordinary silicon at high fields according to most researchersB Intervalley transfer from gamma valley (high mobility) to L valley (low mobility), causing NDRC Impact ionization generating additional electron-hole pairs in the majority of cases studiedD Direct recombination of the conduction electrons with holes as widely reported in standard practiceShow answer & explanation →
Q73.
Lightly doped drain (LDD) structure in short-channel MOSFETs is designed to:
A Increase the overall drive current delivered by the transistor under most conditions encounteredB Reduce hot carrier effects and drain-induced barrier lowering at drain edgeC Increase the threshold voltage required to turn on the device as frequently observed in practiceD Decrease the gate-to-channel capacitance of the transistor in many documented casesShow answer & explanation →
Q74.
The diffusion length of minority carriers L = sqrt(D × tau). In short devices (L<sub>device</sub> << L):
A Most carriers recombine before reaching junction according to conventional understandingB Most carriers reach the junction (low recombination loss)C Diffusion is negligible in routine practice overallD Drift dominates usually in most cases under typical conditionsShow answer & explanation →
Q75.
Threshold voltage roll-off in short-channel MOSFETs occurs because:
A The gate oxide layer becomes progressively thicker as the channel length is shortened according to standard textbooksB Drain depletion charge extends under channel, reducing effective Vth (drain-induced barrier lowering, DIBL)C The gate dielectric layer undergoes a sudden catastrophic electrical breakdown event in general practiceD The substrate doping concentration increases sharply near the shortened channel region as frequently describedShow answer & explanation →
Q76.
When an intrinsic semiconductor is doped with a pentavalent impurity, it becomes:
A n-typeB p-typeC an insulatorD a superconductorShow answer & explanation →
Q77.
A p-n junction diode under forward bias:
A conducts with low resistanceB blocks current completelyC has very high resistanceD acts as a perfect insulatorShow answer & explanation →
Q78.
A Zener diode is normally used as a:
A voltage regulator (in reverse breakdown)B signal amplifierC oscillatorD half-wave rectifier onlyShow answer & explanation →
Q79.
A full-wave rectifier fed with a 50 Hz AC supply produces a ripple in the output at a frequency of:
A 25 HzB 50 HzC 100 HzD 200 HzShow answer & explanation →
Q81.
In a common-emitter transistor amplifier, the phase difference between the input and output voltages is:
Show answer & explanation →