A semiconductor structure, comprising: a III-V substrate structure with a depletion mode transistor device disposed in a first region of the structure and an enhancement mode transistor device disposed in a laterally displaced second region of the structure and a RF/microwave/milli-meter wave transistor device formed in a laterally displaced third region thereof: a channel layer disposed in the substrate structure for the depletion mode and enhancement mode transistor devices; wherein substrate structure includes: an enhancement mode transistor device layer made of InGaP or ZnSe, providing an etch stop layer also serving to provide a Schottky contact layer, such layer being disposed over the channel layer; a first layer disposed on the enhancement mode transistor device layer; a depletion mode transistor device etch stop layer disposed on the first layer; a second layer disposed on the depletion mode transistor device etch stop layer; and wherein: the depletion mode transistor device has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer; the enhancement mode transistor device has a gate recess passing through the second layer, the depletion mode transistor device etch stop layer, the first layer, and terminating in the enhancement mode transistor device layer; and the RF/microwave/milli-meter wave transistor has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer. a III-V substrate structure with a depletion mode transistor device disposed in a first region of the structure and an enhancement mode transistor device disposed in a laterally displaced second region of the structure and a RF/microwave/milli-meter wave transistor device formed in a laterally displaced third region thereof: a channel layer disposed in the substrate structure for the depletion mode and enhancement mode transistor devices; wherein substrate structure includes: an enhancement mode transistor device layer made of InGaP or ZnSe, providing an etch stop layer also serving to provide a Schottky contact layer, such layer being disposed over the channel layer; a first layer disposed on the enhancement mode transistor device layer; a depletion mode transistor device etch stop layer disposed on the first layer; a second layer disposed on the depletion mode transistor device etch stop layer; and wherein: the depletion mode transistor device has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer; the enhancement mode transistor device has a gate recess passing through the second layer, the depletion mode transistor device etch stop layer, the first layer, and terminating in the enhancement mode transistor device layer; and the RF/microwave/milli-meter wave transistor has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer. a channel layer disposed in the substrate structure for the depletion mode and enhancement mode transistor devices; wherein substrate structure includes: an enhancement mode transistor device layer made of InGaP or ZnSe, providing an etch stop layer also serving to provide a Schottky contact layer, such layer being disposed over the channel layer; a first layer disposed on the enhancement mode transistor device layer; a depletion mode transistor device etch stop layer disposed on the first layer; a second layer disposed on the depletion mode transistor device etch stop layer; and an enhancement mode transistor device layer made of InGaP or ZnSe, providing an etch stop layer also serving to provide a Schottky contact layer, such layer being disposed over the channel layer; a first layer disposed on the enhancement mode transistor device layer; a depletion mode transistor device etch stop layer disposed on the first layer; a second layer disposed on the depletion mode transistor device etch stop layer; and wherein: the depletion mode transistor device has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer; the enhancement mode transistor device has a gate recess passing through the second layer, the depletion mode transistor device etch stop layer, the first layer, and terminating in the enhancement mode transistor device layer; and the RF/microwave/milli-meter wave transistor has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer. the depletion mode transistor device has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer; the enhancement mode transistor device has a gate recess passing through the second layer, the depletion mode transistor device etch stop layer, the first layer, and terminating in the enhancement mode transistor device layer; and the RF/microwave/milli-meter wave transistor has a gate recess passing through the second layer and the depletion mode transistor device etch stop layer and terminating on the first layer.