Abstract Room temperature grown β-Sn films were thermally oxidised for 2 hours at various temperatures up to 200°C both in air and in vacuum. Only above about 130°C is α-SnO oxide formed; below 130°C amorphous oxide growth occurs. No higher oxide growth occurs in air. In vacuum, the growth morphology of α-SnO is different (whisker growth). A surprising result — the growth of a higher oxide at reduced oxygen partial pressure — was noted.