Effects of fixed charge on R0A value of ZnS-passivated x=0.3 HgCdTe n-on-p diode are explained as a shunt resistance that affects current-voltage (I-V) and dynamic resistance-voltage (Rd-V) characteristics. The fixed charge of 1×1011/cm2 to 2 × 1011/cm2 which is usually obtained with ZnS passivation makes the surface weakly inverted and reduces HgCdTe diode R0A value owing to the short generation lifetime of HgCdTe substrate. The gate-controlled diode and specially fabricated diode are used to explain the surface leakage current in the weak inversion and charge sheet model is used to explain the characteristics. It is found that the surface leakage current by the inverted channel in the weak inversion can reduce R0A more than other currents such as the generation current and tunneling current which are usually used to explain the surface leakage current of HgCdTe diode.