The subject of this analysis is the institution of the permanent establishment in international tax law. The aim of the article is to present the versions of a service permanent establishment, developed by the OECD and the United Nations, and analyze the relations between the permanent establishment of this type and other types. Despite the general similarities, service permanent establishment models developed by the two largest international economic organizations are not identical. As far as their legal force service permanent establishment is identical to the other types of permanent establishment when introduced into double tax treaty. Service permanent establishment is independent and autonomous from the other types of permanent establishment. For its application by the tax authorities, it is therefore not necessary to apply other provisions. Service permanent establishment, however, can only be applied when no other permanent establishment provisions are applicable in a particular case. Considering on service permanent establishment from this perspective, it follows that it is ancillary under international tax law.