Methods of postcolonial analysis can make a major contribution to refining understandings of modern Thai history and culture. However, the fact that Thailand was not colonised has incited a widespread resistance to postcolonial studies in the field. Conservative Thai studies scholarship dismisses the very possibility of postcolonial analysis of 'never-colonised' Thailand. Even critical scholars who highlight similarities between Thailand and its once-colonised Southeast Asian neighbours doubt that methods based on deconstructing the coloniser/ colonised relation capture the specificity of a society whose history places it outside the strict contours of that binary. This study responds to both the conservative and critical objections to postcolonial analyses of Thailand by revisiting the originally Marxist notion of Thailand as a semicolony of Western empire. It is argued that a post-Marxist reading of Thai semicolonialism can challenge conservative resistance to comparing Thailand to former colonies and also provide a basis for critical dialogue with postcolonial studies. While the Marxist frameworks that gave birth to the notion of semicolonialism lost influence after the end of the Cold War, the term is still widely used in critical Thai studies, although now in a theoretically impoverished form. The aim of this study is to reinvigorate semicolonialism with renewed theoretical force by investigating why the notion has outlived its Marxist origins and specifying the critical work that it continues to do, albeit implicitly, in post-Marxist Thai studies. Such an understanding can provide a basis for a more comprehensive account of imperialism that incorporates the experiences of the empirically significant but still theoretically neglected category of non-Western non-colonies such as Thailand.