Does Shenzhen Education Bureau stipulate that private teacher contracts can be signed for one semester?

You can't. According to the inquiry of official website, the temporary employment of teachers in Shenzhen Education Bureau is generally based on years, at least one year. Even temporary teachers with insufficient supplementary resources need more than one year to ensure the smooth development of school education and teaching. Shenzhen, referred to as Pengcheng for short, is a prefecture-level city under the jurisdiction of Guangdong Province, a city with separate plans, a mega-city and a special economic zone approved by the State Council.