We present an X-ray scattering study on a series of semifluorinated n-alkane (F12Hn) powder samples, with even-numbered hydrocarbon chains n = 6-18. At elevated temperatures the samples appear to have a simple lamellar structure consisting of single-layered stacks. At ambient temperature three different rather complex bulk structures were observed as a function of the chain length of the hydrocarbon molecular moiety. Our results are compared to structure models for F12Hn found in the literature, and some new features of the structure of the room temperature phase are disclosed.