The efficiency η and output power P per unit area were computed for silicon p-n-n
+avalanche diodes having an active region of 5 microns. The condition for making both η and

maximum is that the field at the n-n
+interface generated by impurity and bias voltage is about one fourth of that at the junction under oscillation conditions. The maximum η and

were calculated to be about 20.5 per cent and 53 kW/cm
2. Dc current density J
0for maximum

was about 4200 A/cm
2. On the other hand, J
0for maximum η was calculated to be about 800 A/cm
2. It was found that a diode having an abrupt type junction is the best. The condition under which a diode is represented by use of a diode with abrupt type junction is that the region of a homogeneous field near the junction is less than one fifth of the space-charge region.