The conductance measurements of the non-annealed (D1) and 400 degrees C annealed (D2) Ni/n-GaP/Al diodes were made over a wide frequency range of (10 kHz to 5 MHz) and temperature of (100-320 K with steps of 20 K) with bias voltage as a parameter. The capacitance and conductance measurement method is one of the most popular non-destructive methods to obtain information about metal-semiconductor (MS) diode interfaces. The interface state density distribution curves were determined over the band-gap energy near the semiconductor energy midgap. The interface state density (D-it) has been seen to be of the order of similar to 10(12) eV(-1) cm(-2). The D-it similar to T curves have been plotted for different values of bias voltage. The value of D-it increased with increasing measurement temperature, and with increasing voltage from negative bias to positive bias voltage for both diodes. It was seen that the D-it value for D2 diode was greater than that for the D1 diode at each measurement temperature and bias voltage. It was seen in the interface state energy distribution or density distribution curves that the value of D-it has increased from the valence band maximum (E-v) towards conduction band minimum (E-c) at each measurement temperature.