This paper describes a design of an ultra low-power, low-voltage operational transconductance amplifier (OTA). A two stage OTA is implemented in 0.13 μ m SiGe BiCMOS technology. The OTA operates with all transistors active in subthreshold region. Under the typical operating conditions, circuit supply voltage is 0.5 V, supply current 150 nA and power consumption is 75 nW. Low-frequency gain is 53 dB, gain-bandwidth product (GBW) 350 kHz and phase margin 55°. -1 dB gain compression point is -7.4 dBm and output intercept point (OIP3) -21.5 dBm. OTA layout active chip area is 0.0014 mm2.