Question

why does the resistance of a semiconductor decreases with temperature ?

Answer 1

in semi conductors number of free electrons is less.free electron are responsible for conductivity.so when the temperature is increased the electrons from the low energy level jump to higher energy level.due to which conductivity increases.if conductivity increases that means resistivity decreases

The number (conductivity) is proportional to the Boltzmann factor e^-Eg/RT, where Eg is the energy gap . The conductivity of a semiconductor therefore increases exponentially with an increase in temperature.