Using a number of localized sensors and actuators, a feedback controller is designed in order to reduce the growth of three-dimensional disturbances in the hotplate boundary layer. A reduced-order model of the input-output system (composed of the linearized Navier-Stokes equations including inputs and outputs) is computed by projection onto a number of balanced truncation modes. It is shown that a model with 50 deuces of freedom captures the input-output behavior of the high-dimensional (n similar to 10(7)) system. The controller is based on a classical LQG scheme with a row of three sensors in the spanwise direction connected to a row of three actuators further downstream. The controller minimizes the perturbation energy in a spatial region defined by a number of (objective) functions.