There is disclosed a hydrothermally stable microporous crystalline material comprising a molecular sieve or zeolite having an 8-ring pore opening structure, such as SAPO-34 or aluminosilicate zeolite, able to retain a specific percentage of its surface area and micropore volume after treatment with heat and moisture, such as at least 80% of its surface area and micropore volume after exposure to temperatures of up to 900.degree. C. in the presence of up to 10 volume percent water vapor for a time ranging from 1 to 16 hours. Methods of using the disclosed crystalline material, such as in the SCR of NO.sub.x in exhaust gas are also disclosed, as are methods of making such materials.