A novel maize variety designated X75K308 and seed, plants and plant parts thereof are produced by crossing inbred maize varieties. Methods for producing a maize plant by crossing hybrid maize variety X75K308 with another maize plant are disclosed. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into X75K308 through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. This invention relates to the maize variety X75K308, the seed, the plant produced from the seed, and variants, mutants, and minor modifications of maize variety X75K308. This invention further relates to methods for producing maize varieties derived from maize variety X75K308.