High performance GaAs MESFETs have been fabricated on epitaxial layers grown by MO-CVD (metal-organic chemical vapor deposition). At 8 GHz, a NF (noise figure) of 1.8 dB with an associated gain of 11 dB has been obtained for Al-gate MESFETs with gate dimensions of 0.5 × 300 µm. The NF at 8 GHz is lower by 1 dB than the previously reported results on MESFETs prepared by MO-CVD (1). The substantial improvement of the device performance is due to the first successful growth of thick enough buffer layer, together with an extremely sharp interface profile of electron concentration between a buffer and an active layers.