A semiconductor is subjected to an electric field. Suppose the...

When the temperature of a semiconductor is increased, more covalent bonds are broken due to thermal energy. This leads to an increase in the number of electron-hole pairs, so the number of charge carriers $n$ increases.

The average drift speed of charge carriers is given by $v = \mu E$, where $\mu$ is the mobility and $E$ is the applied electric field. The mobility is given by $\mu = \dfrac{e \tau}{m}$, where $\tau$ is the relaxation time.

As temperature increases, the thermal agitation of lattice ions increases, causing charge carriers to collide more frequently. This decreases the relaxation time $\tau$.

Since $\tau$ decreases, the mobility $\mu$ decreases, which in turn causes the average drift speed $v$ to decrease.

Therefore, $n$ increases but $v$ decreases.