According to the specs of a 64x2 3800+ AM2, you need a hsf that can handle 65W without going over 55c to 72c max, the sempron 3000+ 754 hsf requirement is 69c max at 62W. It looks like the AM2 socket only has 2 outside tabs for the heatsink fan; compared to 6 tabs on the 754 socket? The 754 heatsink should fit the AM2 socket, using the center tab's but the heatsink spring retainer might overload the tabs on the socket since it's only using 2 rather than 6. I have a spare a64 socket bracket with backing plate that has 6 tabs, along with an all aluminum thinfin a64/opteron fx rated heatsink/fan, was using it on an a64 3400+, it's dynatron part number A21, if you want it let me know, I'll send it for the price of shipping, the heatsink needs lapped because it got scratched up.. Any whoo your's should work fine if you are not overclocking, just keep a close eye on the temps. You'll see the lowest max load temps, once the heatsink compound settles in, after a few heat cycles. If temps are below 50c at max load, it'll work.