2S[ABCDFHJK] are Japanese transistors/FETs. "2" is the number of junctions (hence diodes start with "1S"), A and B are PNP while C and D are NPN. A and C are usually for high frequency and C and D are for low frequency purpose but the distinction is not clear these days.
2SF devices are thyristers/SCRs, 2SH are uni-junction transistors.
2SJ and 2SK are P-channel and N-channel FETs, respectively. Both JFETs and MOSFETs are registered here.
The numbers are registration number (sequential) at JEITA. The alphabet after the number indicates a revision (like popular 2SK30A).
Toshiba uses rainbow colors for ranks eg. O(range), Y(ellow), GR(een), BL(ue), V(iolet), etc. NEC used alphabet, L, M, etc.
I> am a new user in transistors, another numbering method like 2SA, B, C, D, F, H, --- ETC. does anybody guide me to the net or web where these explanations are.??? Thanks.