In this paper, a novel optically-activated cascode structure is proposed to be used with a normally -on gallium nitride (GaN) field-effect transistor (FET) device to achieve an overall normally off configuration. Using this novel configuration, cost-effective infrared (IR) lasers can be utilized instead of expensive ultraviolet (UV) lasers to activate this structure which includes a widebandgap-material device (GaN FET). Furthermore, the effect of parasitic inductance available in the package and connections of this proposed configuration is evaluated using Silvaco TCAD simulations. In practice, one high-power normally-on FET device is connected in series with a low-power optical switch (OS) to make the proposed overall normally-off cascode structure. The capability of being optically-activated for the proposed structure has many advantages over the conventional electrically-activated cascode structures including but not limited to: more immunity to electromagnetic interference (EMI), using only one main bias as the power source, using cost-effective long-wavelength laser instead of expensive short-wavelength lasers to trigger the GaN devices, reduced current and voltage ringing during switching transitions, etc. Comprehensive device modeling and parasitic inductance analysis for this new proposed optical cascode GaN FET device are provided in this work.