The arguably uniquely human ability to derive hierarchical syntactic structures from linear sequences of words has been claimed to be central to language comprehension in linguistic theories. However, the real-time processing of syntax and its relation to semantics remain disputed, especially regarding the effect of the hypothesized hierarchical relations among words over linear relations. Research on semantic processing has made extensive use of priming paradigms to study online access and retrieval of meaning. Extension of these paradigms to sentence contexts, however, has yielded mixed results, especially regarding the influence of syntactic relations. In the present self-paced reading study, we used grammatical, meaningful sentences to investigate how the syntactic relations and linear distance between prime and target words influence semantic priming effects, as reflected in target word reading times of 64 native speakers of English. Each participant read 160 experimental sentences, each followed by a Yes-No comprehension question. Experimental sentences contained a prime and a target word with two levels of semantic association (high vs. low association, e.g., ‘mistress’ - ‘affair’ vs. ‘actress’ - ‘affair’). Crucially, we varied the structure between the prime and the target, both in terms of (1) the number of intervening words (linear distance, 2 vs. at least 4 words) and (2) number and type of intervening syntactic nodes (syntactic relation). Linear mixed effects models revealed semantic priming when the prime and target were in a direct syntactic relation, and interference effects when they were in an indirect relation, both at short and long linear distances. The strength of these effects was correlated with semantic priming effects found in a word pair relatedness judgement task, as well as with digit span results measuring working memory capacity. These results suggest that structural relationships modulate within-sentence semantic priming while linear distance only plays a marginal role. We interpret these results in the context of cue-based retrieval parsing theories. Related primes facilitate semantic integration when in a direct syntactic relationship with the target but may be incorrectly integrated with the target noun and lead to interference effects when in an indirect relation. Syntactic processes participate in the creation of a hierarchically structured representation of the sentence that implements specific relations between words and that guides the real-time semantic processing of each incoming word.