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Organic semiconductors are the key component in organic electronics and determine the device performance. There is great interest in the fundamental understanding of charge-transport mechanisms and the structure–property relationships in organic semiconductors.1 To explore the intrinsic charge-carrier transport properties of organic semiconductors, the most promising method is to fabricate a single-crystal field-effect transistor (FET) because the organic single crystal has perfect molecular order, is free of grain boundaries, and has a minimal concentration of charge traps.2 Up to now, there has been significant progress in the growth of organic single crystals, the fabrication of single-crystal FETs, and the investigation of the structure–property relationship of organic semiconductors.3, 4 However, to fully understand the charge transport mechanisms, it is necessary to investigate the anisotropy of charge transport in organic semiconductor single crystals, because the anisotropic molecular packing in the crystals can lead to a strong anisotropy in the field-effect mobility. To date, the anisotropic charge transport properties of a few organic single crystals have been measured. For example, Sundar et al., Reese and Bao, and Zeis et al. succeeded in measuring the mobility anisotropy in single-crystal rubrene (5,6,11,12-tetraphenyltetracene).5 Mannsfeld et al. measured the anisotropic field-effect mobility of dicyclohexyl-α-quaterthiophene (CH4T) single crystals.6 Li et al. fabricated transistors based on individual microcrystals with multichannels along different crystal axes and crystal planes by using a “two-dimensional organic ribbon mask” technique to probe the charge-transport anisotropy.7 The anisotropic field effect mobilities of pentacene and tetracene were also studied.8, 9 However, all of the above results cover only one- and two-dimensional charge transport anisotropy, which is not enough to provide sufficient insight into the correlation between molecular packing and charge transport in organic semiconductor materials because many crystals have a three-dimensional (3D) nature. Therefore, it is necessary to investigate the 3D charge transport anisotropy in organic semiconductors. In this Communication, we report on the 3D charge transport anisotropy in organic semiconductor single crystals. By controlling the growth conditions, single crystals can be grown either parallel or perpendicular to the substrate.10 These two types of morphology provide a good platform for the fabrication of differently oriented transistor devices and for the investigation of 3D charge transport in organic semiconductor single crystals (Figures 1a,d).