The efficiency, negative resistance, and conditions for space-charge control relevant to operation of a bulk semiconductor diode in the limited space-charge accumulation (LSA) mode of oscillation are discussed. Numerical results for n-GaAs indicate a maximum dc to rf-conversion efficiency of 18.5% for sine-wave excitation. The usable range of doping to frequency for n-GaAs is found to be 2×104 to 2×105 sec/cm3 with an optimum value of about 6×104 sec/cm3. Although a reduction in efficiency at frequencies above 100 GHz is expected due to the finite response time of GaAs, worthwhile efficiency may be obtained at several hundred GHz.