Understanding sources of judicial bias is essential for establishing due process. To date, theories of judicial decision making are rooted in ranked societies with majority–minority group cleavages, leaving unanswered which groups are more prone to express bias and whether it is motivated by in-group favoritism or out-group hostility. We examine judicial bias in Kenya, a diverse society that features a more complex ethnic landscape. While research in comparative and African politics emphasizes instrumental motivations underpinning ethnic identity, we examine the psychological, implicit biases driving judicial outcomes. Using data from Kenyan criminal appeals and the conditional random assignment of judges to cases, we show that judges are 3 to 5 percentage points more likely to grant coethnic appeals than non-coethnic appeals. To understand mechanisms, we use word embeddings to analyze the sentiment of written judgments. Judges use more trust-related terms writing for coethnics, suggesting that in-group favoritism motivates coethnic bias in this context.