Well, Han Chinese is a ethnicity. Different from nationality but I think culturally they all same same.
Here are the percentages of Han Chinese in China, Hong Kong, Taiwan, and Singapore:
China: Approximately 92% of the population is Han Chinese.
Hong Kong: About 92% of the population is Han Chinese.
Taiwan: Around 95-98% of the population is Han Chinese.
Singapore: About 74% of the population is Han Chinese.