We have studied the microstructure dependence of He bubble formation in silicon carbide. Helium accumulation in SiC was performed by 500 keV (3)He implantation at room temperature with a fluence of 5 x 10(15) cm(-2). Depth concentration profiles have been investigated in 6H-SiC single crystals and alpha-SiC polycrystals by NRA spectrometry. Cross-sectional TEM samples have been imaged to study bubble formation. After annealing at 1300 degrees C, results clearly demonstrate an influence of grain boundaries on He retention yield in a-SiC polycrystals while helium is totally released from single crystals. Polycrystals also display the formation of intragranular overpressurized bubbles while no bubbles are observed in single crystals. Interpretations are proposed on the basis of the nature of He traps. (C) 2009 Elsevier Ltd. All rights reserved.