A new active microstrip reflectarray element (unit cell) with an internal microwave integrated circuit amplifier is introduced. The amplifier resides in a small slot within the footprint of the square patch antenna and is connected between the feed points of the patch's orthogonal polarizations. This element results in reduced array element spacing, reduced transmission line losses through elimination of long feed lines, and a simplified fabrication process compared to other active reflectarray unit cells. Patch geometries with several slot shapes are studied with simulations to arrive at an antenna configuration with good return loss and isolation characteristics. The stability and gain of the system are analyzed over frequency. Measured radiation pattern and gain data for a single element and a small array agree well with predictions and demonstrate the element's capabilities. Limitations of the active element, approaches to mitigate these limitations, and directions for future work are discussed.