Title: Semi-Supervised Speech-Language Joint Pre-Training for Spoken Language Understanding. Abstract: Spoken language understanding (SLU) requires a model to analyze input acoustic signals to understand its linguistic content and make predictions. To boost the models' performance, various pre-training methods have been proposed to utilize large-scale unlabeled text and speech data. However, the inherent disparities between the two modalities necessitate a mutual analysis. In this paper, we propose a novel semi-supervised learning method, AlignNet, to jointly pre-train the speech and language modules. Besides a self-supervised masked language modeling of the two individual modules, AlignNet aligns representations from paired speech and transcripts in a shared latent semantic space. Thus, during fine-tuning, the speech module alone can produce representations carrying both acoustic information and contextual semantic knowledge. Experimental results verify the effectiveness of our approach on various SLU tasks. For example, AlignNet improves the previous state-of-the-art accuracy on the Spoken SQuAD dataset by 6.2%.