This part is a kind of semiconductor called 55N03LTA.
Function of this product has Logic Level FET.
Manufacturers : Philips
Image and pinout :
Some of the text within the PDF file :
PHP/PHB/PHD55N03LTA TrenchMOS™ Logic Level FET Rev. 04 — 4 September 2002 Product data 1. Description N-channel logic level ﬁeld-effect power transistor in a plastic package using TrenchMOS™ technology. Product availability: PHP55N03LTA in a SOT78 (TO-220AB) PHB55N03LTA in a SOT404 (D2-PAK) PHD55N03LTA in a SOT428 (D-PAK). 2. Features s Low on-state resistance s Fast switching. 3. Applications s Computer motherboard high frequency DC to DC converters. 4. Pinning information Table 1: Pinning - SOT78, SOT404, SOT428 simpliﬁed outlines and symbol Simpliﬁed outline mb mb mb Pin Description 1 2 3 mb gate (g) drain (d) source (s) mounting base, connected to drain (d)  Symbol d g s 2 2 1 MBK106 MBB076 1 3 MBK116 3 MBK091 Top view 1 2 3 SOT78 (TO-220AB)  SOT404 (D2 [ ... ]