The temperature (T) dependence of resistivity $\left(\rho \right)$ of semiconductor is represented by

The variation of specific resistance with temperature is as follows $\rho ={\rho }_{net}+\left[1+\alpha \left(\text{T}-{\text{T}}_{\text{net}}\right)\right]$

Where $\rho =$ specific resistance at temperature T, 

${\rho }_{net}=$Specific resistance of reference temperature

$\alpha =$Temperature of coefficient of resistance

 Rearranging the terms we have

$\rho ={\rho }_0+{\rho }_0\alpha \left(\text{T}-{\text{T}}_{\text{0}}\right)$

On comparing the equation with equation of straight line$y=\text{m}x+\text{c}$, we have the slope negative

Note: The temperature coefficient of resistance of semiconductors is negative that is their electrical resistance decreases (or conductivity increases) with rise in temperature. At absolute zero a semiconductor behaves as an ideal insulator.