The authors achieved considerable suppression of surface segregation of Si dopants in In0.75Ga0.25As/In0.52Al0.48As high electron mobility transistor (HEMT) structures grown on (411)A InP substrates by molecular beam epitaxy (MBE). The (411)A HEMT structures were conventionally grown at a high substrate temperature (T-s) of 540 degrees C in order to form the extremely flat (411)A heterointerfaces. This results in considerable surface segregation of Si dopants. Surface segregation of Si dopants was suppressed by lowering growth temperature of the top InAlAs barrier layer (T-B) down to 450 degrees C with keeping T-s of 540 degrees C for other parts. Sheet carrier concentration (N-s) of two-dimensional electron gas (2DEG) was measured as a function of thickness (L-b) of the top InAlAs barrier for T-B=450 and 540 degrees C samples. Observed N-s of the T-B=540 degrees C sample vanished when L-b approached to 7 nm, while 2DEG with of N-s similar to 2 x 10(12) cm(-2) remained for the T-B=450 degrees C sample. Surface segregation of Si-sheet-doped (411)A InAlAs layers grown at T-B was also characterized by secondary ion mass spectrometry measurements. Si segregation length (lambda(Si) : 1/e decay length of Si concentration) observed for T-B=450 degrees C sample was 2.3 nm, which is 56% smaller than that for T-B=540 degrees C (lambda(Si)=5.2 nm). (c) 2006 American Vacuum Society.