The pressure-induced phase transition in the Polk and Connell-Temkin type models of amorphous $\mathrm{GaAs}$ 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 $\mathrm{Ga}$ and $\mathrm{As}$ atoms. It is found that chemically disordered $\mathrm{Ga}$ 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.