This part is a kind of semiconductor called BF1012S.

Function of this product has Silicon N-Channel MOSFET Tetrode (For low noise/ high gain controlled input stages up to 1GHz Operating voltage 5V Integrated stabilized bias network).

Manufacturers : Siemens Semiconductor Group

Image and pinout :

Some of the text within the PDF file :

BF 1012S Silicon N-Channel MOSFET Tetrode • For low noise, high gain controlled input stages up to 1GHz • Operating voltage 5V • Integrated stabilized bias network ESD: Electrostatic discharge sensitive device, observe handling precaution! Type Marking Ordering Code Q62702-F1627 Pin Configuration 1=S 2=D 3 = G2 4 = G1 Package SOT-143 BF 1012S NYs Maximum Ratings Parameter Drain-source voltage Symbol Value 16 25 10 3 200 -55 ...+150 150 Unit V mA V mW °C VDS ID ±I G1/2SM +VG1SE Continuos drain current Gate 1/gate 2 peak source current Gate 1 (external biasing) Total power dissipation, T S ≤ 76 °C Storage temperature Channel temperature Ptot T stg T ch Thermal Resistance Channel - soldering point Rthchs ≤370 K/W Note: It is not recommended to apply external DC-v [ ... ]

BF1012S PDF Datasheet Download