In hadron phenomenology, diquark structures can be an important degree of freedom in certain configurations. We investigate the possibility that the diquark structure can be treated as an elementary field in certain configurations. To start with, we assume that Λ is composed of a spectator strange quark and a diquark. We construct a QCD sum rule for Λ, where the input parameters are the diquark mass and its condensate, in addition to other parameters of QCD sum rules. We find good Borel curve for the Λ mass for certain combinations of the diquark mass and condensate, and that smaller diquark condensate is needed when the diquark mass is increased to maintain the good Borel curve. The same sets of diquark mass and condensate are found to work well for Λc and Λb.