User interface prototyping is an efficient approach for eliciting user requirements in the early phase of software development. It is an iterative analysis technique in which users are actively involved in the mocking-up of the UI for a system. It is typically done in a drag-and-drop fashion by professionals, which is time-consuming and requires specialized knowledge. This paper presents a prototype tool SAIP (Semi-Automatic software user Interface Prototyping), which allows users to express their natural language requirements and semi-automatically generates a corresponding graphical user interface. Based on a systematic literature review of the user interface prototype, we design a framework that maps natural language to the user interface prototype. Furthermore, develop a demo version of the SAIP - a user interface prototyping software served from natural language processing and neural network for the user interface automatic generation. Our tool aims to help users who have little knowledge in user interface design to express their ideas and requirements freely.