A cover glass for semiconductor package having thermal expansion coefficient conformable to plastic packages and allowing accurate detection of existence of foreign substances, dusts, etc. in an imaging test always having a low emission amount of alpha-ray, and a related production method. The cover glass comprises, in terms of percentage by mass, of from 58 to 75% of SiO2, of from 1.1 to 20% of Al2O3, of from 0 to 10% of B2O3, of from 0.1 to 20% of Na2O, of from 0 to 11% of K2O, and of from 0 to 20% of alkaline earth metal oxide. The cover glass has average thermal expansion coefficient of from 90 to 180×10−7/° C. in the temperature range of from 30 to 380° C., a Young's modulus of 68 GPa or more, and an emission amount of alpha-ray from the glass of 0.05 c/cm2·hr or less.