The semiconductor does not obey Ohm's law because it has opposite properties than a conductor and it has non-linear properties. Let's explain in detail.

We know that according to Ohm's law, the flow of current through a conductor is directly proportional to the potential difference between the two ends of that conductor when temperature and other physical quantities are constant.

So according to Ohm's law,

V I

Where V= voltage or potential difference
I = Current

According to Ohm's law, the VI characteristics are given below,

So as you see in the above graphical diagram according to Ohm's law the changes in current with voltage should be linear.

Now let's talk about the semiconductor. A semiconductor has a non-linear property. If we see the VI characteristics of the normal PN Junction diode which is a semiconductor device, then we will see the VI characteristics of the Diode are nonlinear.

So for the non-linear characteristics, Semiconductor does not obey Ohm's Law.

Another Reason,

When the temperature of the semiconductor is increased then the covalent bonds break quickly, as a result, the free charge carriers increase. So more electrons coming from the valence band to the conduction band. So it is clear that when the temperature increases the conduction of the semiconductor increases and resistance decreases.

But in the case of a conductor, the resistivity increases with increasing temperature. So the temperature vs resistivity property of conductor and semiconductor is completely opposite. This may be a reason of Semiconductor does not obey Ohm's Law.