Title: Reducing the Capacity Gap via Spherical Knowledge Distillation. Abstract: Knowledge distillation aims to obtain a small and effective student model by learning the output from a large knowledgeable teacher model. However, when the student is distilled by an oversized teacher, a critical performance degradation problem is exposed. This paper revisits performance degradation problem from the perspective of model confidence. Specifically, we apply energy-based metrics to measure the confidence of models, and propose Spherical Knowledge Distillation (SKD): a more efficient knowledge distillation framework when distilling with larger teachers. A theoretical analysis is provided to show that SKD can effectively reduce the confidence gap between the teacher and student, thus alleviating the performance degradation problem. We demonstrate that SKD is easy to train, and can significantly outperform several strong baselines on various mainstream datasets, including CIFAR-100 and ImageNet. 