This paper proposes a 20 mW class low-power and miniaturized oven controlled crystal oscillator (OCXO) by combination of the following two methods. (1) A crystal resonator and a CMOS-LSI for oscillation and oven control circuits are integrated for realizing an integrated OCXO chip. (2) The integrated chip is connected with thin film metal interconnection on a thin polyimide film and is suspended by an ultrasonic bonding technique in vacuum packaging. Based on the thermal analysis, we designed the thermally isolated connection. Experimental results showed that the fabricated OCXO successfully saved about 90% power consumption compared with the existing wire bonding implementation.