For semiconductor material, current flow is both due to electrons and holes (however in practice, it the electron which moves), we can write

......................(3.6)

and are respectively the density and mobility of holes.
The point form Ohm's law can be used to derive the form of Ohm's law used in circuit theory relating the current through a conductor to the voltage across the conductor.
Let us consider a homogeneous conductor of conductivity , length L and having a constant cross section S as shown the figure 3.1. A potential difference of V is applied across the conductor.

Fig 3.1: Homogeneous Conductor