German citizens can travel to Hong Kong for a period of up to 90 days without a visa. After leaving (e.g. to Macau, or to the Republic of China with a visa you have already obtained in Germany), you may immediately be permitted an additional 90-day stay in Hong Kong without a visa. In this case, it is a prerequisite that the first time you enter Hong Kong your passport be valid for at least six more months.
(Source: http://www.auswaertiges-amt.de/DE/Laenderinformationen/00-SiHi/HongkongSicherheit.html)