GaAs microwave monolithic ICs with novel on-chip BST (Ba x Sr 1-x TiO 3 ) capacitors are demonstrated. MOD (Metal Organic Decomposition) technique was employed to make the BST thin film. The fabricated BST capacitor has the dielectric constant as high as 300, which is 50 times higher than the conventional Si 3 N 4 one. The implemented GaAs MMIC with on-chip BST capacitor provides both high gain and low power dissipation characteristics. These MMIC can be packaged in a compact outline with reduced pin counts. BST capacitors also show the suppressed harmonics due to their low-pass filtering characteristics of the frequency roll-off around 2 GHz. The present technology will reduce the system size for a variety of the mobile communication systems.