Silicon-photonic link technology promises to satisfy the growing need for high bandwidth, low-latency and energy-efficient network-on-chip (NoC) architectures. While silicon-photonic NoC designs have been extensively studied for future manycore systems, their use in massively-threaded GPUs has received little attention to date. In this paper, we first analyze an electrical NoC which connects different cache levels (L1 to L2) in a contemporary GPU memory hierarchy. Evaluating workloads from the AMD SDK run on the Multi2sim GPU simulator finds that, apart from limits in memory bandwidth, an electrical NoC can significantly hamper performance and impede scalability, especially as the number of compute units grows in future GPU systems.To address this issue, we advocate using silicon-photonic link technology for on-chip communication in GPUs, and we present the first GPU-specific analysis of a cost-effective hybrid photonic crossbar NoC. Our baseline is based on an AMD Southern Islands GPU with 32 compute units (CUs) and we compare this design to our proposed hybrid siliconphotonic NoC. Our proposed photonic hybrid NoC increases performance by up to 6× (2.7× on average) and reduces the energy-delay 2 product (ED 2 P) by up to 99% (79% on average) as compared to conventional electrical crossbars. For future GPU systems, we study an electrical 2D-mesh topology since it scales better than an electrical crossbar. For a 128-CU GPU, the proposed hybrid silicon-photonic NoC can improve performance by up to 1.9× (43% on average) and achieve up to 62% reduction in ED 2 P (3% on average) in comparison to mesh design with best performance.