Disclosed is a sol-gel process for making high-density monolithic alpha-alumina articles. Cracking problems caused by shrinkage of the gel during the drying and firing stages are minimized by controlling the temperature and humidity during the drying process and by using molds formed of prescribed polymeric materials, preliminarily coated with a silicone release agent. The process of the invention provides porous alpha-alumina articles having a controlled microstructure and a controlled pore size distribution, which are beneficial features when the material is used in practical applications, e.g., as substrates for gas sensors.