Abstract: Generalizing the medical image segmentation algorithms to unseen domains is an important research topic for computer- aided diagnosis and surgery. Most existing methods require a fully labeled dataset in each source domain. Although (Liu et al. 2021b) developed a semi-supervised domain general- ized method, it still requires the domain labels. This paper presents a novel confidence-aware cross pseudo supervision algorithm for semi-supervised domain generalized medical image segmentation. The main goal is to enhance the pseudo label quality for unlabeled images from unknown distribu- tions. To achieve it, we perform the Fourier transformation to learn low-level statistic information across domains and augment the images to incorporate cross-domain information. With these augmentations as perturbations, we feed the input to a confidence-aware cross pseudo supervision network to measure the variance of pseudo labels and regularize the network to learn with more confident pseudo labels. Our method sets new records on public datasets, i.e., M&Ms and SCGM. Notably, without using domain labels, our method surpasses the prior art that even uses domain labels by 11.67% on Dice on M&Ms dataset with 2% labeled data.Code is available at https://github.com/XMed-Lab/EPL SemiDG.