Integrating LLMs for data processing enables semantic querying but causes GPU memory bottlenecks and redundant computations. We present SemInfer, an acceleration system for batch semantic processing that treats the KV Cache as a semantic index, offloading pre-computed caches to host storage to eliminate redundancy. To reduce the index size, we propose a pruning strategy based on last-layer aggregated attention to accurately retain critical semantic tokens. Furthermore, we employ a pipeline mechanism to enable the asynchronous overlapping of CPU-GPU transmission and inference computation. This demonstration showcases the complete workflow of SemInfer on the IMDB dataset, achieving up to a 16.3x inference speedup over direct LLM inference and a 90% reduction in index size with few semantic accuracy loss.