Preparation of crystalline silicoaluminophosphates

A process for preparing a microporous crystalline silicoaluminophosphate, the pores of which are uniform and have nominal diameters of greater than about 3 Angstroms, said process comprising forming an aqueous reaction mixture containing sufficient sources of SiO.sub.2, Al.sub.2 O.sub.3, P.sub.2 O.sub.5 and an organic templating agent and crystallizing the reaction mixture thus formed at a temperature of at least 100.degree. C. until crystal of silicoaluminophosphate are formed, wherein said reaction mixture further contains a source of fluoride ions in an amount sufficient to complex with silicate in the reaction mixture, whereby the release of silicate into the reaction mixture is controlled according to the mass action law.