The pressure-induced phase transition in the Polk and Connell-Temkin type models of amorphous GaAs is studied using ab initio constant-pressure relaxation simulations. Both networks continuously transform from a semiconducting low density amorphous phase to a metallic high density amorphous phase with increasing pressure. The transition is associated with a change from fourfold to sixfold coordination of Ga and As atoms. It is found that chemically disordered Ga atoms behave as nucleation centers for the gradual phase transition in the networks. The pressure-induced changes in the electronic and vibrational properties are studied with details.