A 5 GHz GaAs Monolithic astable multivibrator type voltage controlled oscillator has been developed. The monolithic oscillator uses 2 µm long self aligned TiW-silicide gate MESFETs, and GaAs Shottky diodes for capacitance. Good agreement between the experiment and calculations for oscillation frequency characteristics versus control voltage, is obtained by assuming donor density in the FET active layer to be a Gaussian distribution. This oscillator is useful for monolithic front ends and phase-locked oscillators used in microwave signal processing. X band oscillation frequency will be able to obtained with 1 µm long gate FET and low loss resonance inductors.