The paper proposes scaling effect of number of fingers (N) and effective gate width (w _eff ) on model parameters and subsequently investigate the effect on RF performance characteristics of GaN High electron mobility transistor(HEMT). The device scaling relations in terms of model parameters and RF performance metrics are proposed for two multi-finger HEMTs of 2×200 μm and 4×100 μm respectively. The unity gain current frequency (f _t ) is found to be approximately constant with very negligible increase while maximum unilateral gain frequency (f _max ) increases with increase in number of fingers (N) provided that effective gate width (w _eff ) remain constant. The whole investigation is based on accuracy of the parameter extraction procedure and small signal model developed using pinch-off and de-embedding structures. However, the effective width of both the HEMTs is equal.