To satisfy the requirement of microarray fabrication in optical sensing applications, we report a palm-sized UV LED crosslinker. By employing a microcontroller and the Wi-Fi communication technique, a sequence of different wavelengths, irradiation intensities, and crosslinking durations can be programmed by an Android app. To evaluate the irradiation uniformity of the crosslinker, we immobilized an array of fluorescent-labeled proteins on a silver substrate of high flatness by the reported crosslinker in 8 s and measured the fluorescence intensity throughout the array. For protein spots of the same concentration, the intensity difference is around 10% of the average value. The results show that the reported UV LED crosslinker can help to achieve the uniform and efficient immobilization of a protein microarray.