A gene (GenBank AF096282) coding for a $alpha$-glucosidase (TcaAG, EC 3.2.1.20) from Thermus caldophilus GK24 was expressed in Saccharomyces cerevisiae, a generally recognized as safe (GRAS) host. The thermostable $alpha$-glucosidase was produced inside of the GRAS host at 0.04 unit/mg-dry cell by the constitutively expressing ADH1 promoter and at 1.2 unit/mg-dry cell by the inductively expressing GALl0 promoter, respectively. No $alpha$-glucosidase activities were found in the medium when the MF-alpha signal sequence from S. cerevisiae or $alpha$-amylase signal sequence from Aspergillus oryzae were fused before the $alpha$-glucosidase gene for the secretion.