FS14SM-12 Mitsubishi Electric company original Japan. 

N-Channel Power MOSFET, rDS (ON) (MAX) 0.60Ω, Vdss 600V, Id 14A, Pd 250W, 
High-Speed Switching Use, 

Case type: TO-3P
1-GATE 2-DRAIN 3-SOURCE 4-DRAIN

APPLICATION: 
SMPS, DC-DC Converter, battery charger, power supply of printer, copier, HDD, FDD,
TV, VCR, personal computer etc.