The present study is concerned with the experimental investigation of novel complex surface treatments as a passive trailing edge noise control technique. The proposed novel three-dimensional surface treatments, composed of a combination of finlets with different spacings and patterns, have shown better aeroacoustic performance than the standard two-dimensional treatments in terms of the reduction in the surface pressure power spectral density, the spanwise length-scale, eddy convection velocity, and the trailing edge noise. Furthermore, the boundary-layer flow measurements downstream of the surface treatments have provided some insight into the mechanisms through which three-dimensional surface treatments affect the flow structures, which can help improve the performance of such passive techniques for the suppression airfoil noise at source. The aerodynamic performance of the plates fitted with different surface treatments is also examined using the boundary-layer velocity information. The results from this fundamental study can lead to the development of new generations of quieter airfoils with unconventional surface treatments.