A study has been made on the effects of hydrostatic pressure at room temperature on peak currents Ip, valley currents lv, peak voltages Vp, valley voltages Vv and the exponential excess currents Ix of several narrow GaAs P-N junctions. The pressure ranges from the atmospheric pressure up to 18000 Kg/cm2.The exponential decrease of the peak voltage Vp and the slope S of the exponen-tial excess current (S=(dlnIx)/dV) with the increase of pressure can be explained in termsof the pressure variations of the effective mass of GaAs. It is suggested therefore that pressure dependences of both the energy gap and the effective mass should be taken into account in analyzing the pressure dependent tunneling data of the highly degenerate GaAs P-N junctions. A brief discussion has also been made on the other experimental results.