A novel observation of a highly ordered self-assembled monolayer of ethanethiol (a very short-chain alkanethiol) on Au(111) is reported. A good structural perfection of the monolayer allowed a surprisingly high-resolution STM imaging clearly uncovering the unique 3 x 4 unit cell and the detailed atomic arrangement therein. Along with the infrared reflection absorption spectrum of the monolayer the results indicate that the interchain interactions involving such short alkyl chains can still play a dominant role in controlling the overall monolayer structure.