Does international R&D collaboration produce patents of higher technological value? Applied to the case of Siemens, this paper utilizes the Patent Cooperation Treaty (PCT) and Google Patents statistics to identify patterns within invention and co-invention. For example, sole patenting by headquarters or subsidiaries is juxtaposed with co-invented patent filings, vertical versus horizontal co-patented applications and internal versus external. The paper compares the effect of different forms of co-invention on the technological value of patent filings, proxied by forward external citations. The results are based on 2013 and 2019 Siemens PCT data and confirm the positive effect of international co-invention, vis-à-vis sole patenting, on the technological value of patents. Patent applications co-invented by foreign subsidiaries, or vertically collaborated applications, create higher technological value, while headquarters or single subsidiaries generate fewer forward citations. Moreover, co-patenting by subsidiaries with external partners creates higher technological value than sole patenting by headquarters. Siemens has recognized the value of partnerships with outside inventors and leveraged these relationships in order to generate higher technological value. We contribute by building a unique and detailed classification of co-patenting patterns, and the paper develops a strong case for cross-country co-patenting, especially with external partners. From a managerial perspective, international co-patenting involving external partners has strategic value and must be fostered.