This study examines the correlation between interface roughness and charges. Atomic force microscopy (AFM) and a newly developed area roughness function which couples two roughness parameters, root-mean-square (rms) and fractal dimension (D-F), are used to reliably and accurately characterize surface roughness. Interface charges (D-it and Q(f)) are measured using high frequency and quasistatic capacitance-voltage methods. This study is divided into three parts where smooth, purposely roughened, and purposely smoothened Si substrates are used to make metal-oxide-semiconductor capacitors for measurements. Purposely roughened substrates are obtained using a chemical acid etch solution. Purposely smoothened substrates are initially roughened with the chemical acid etch solution and smoothened through thermal oxidation. We report that the increases of D-it and Q(f) with Si roughness are due entirely to the area increase and orientation changes the result from roughness.