The invention provides a contact lens manufacturing method for cast-molding of silicone hydrogel contact lenses having enhanced oxygen permeability without adversely affecting desirable lens mechanical properties (e.g., modulus). A method of the invention comprises adding a small amount of a radical scavenger (e.g., H-TEMPO) in a polymerizable composition for cast-molding of SiHy contact lenses) to provide the resultant polymerizable composition with a bi-phase curing profile at a curing temperature of from about 45° C. to about 100° C. With such a bi-phase curing profile, the resultant polymerizable composition can be thermally cured at the curing temperature to form a SiHy contact lens having an oxygen permeability higher than that for a polymerizable composition having the substantially identical composition excepting being free of any radical scavenger.