Based on the large statistics sample collected by the FOCUS experiment
at FNAL, we obtained interesting results on semileptonic decays of charm
mesons. First, I will show you the interference pattern found in D+ -> K
pi mu nu, between the dominant K*0(980) resonance and a broad S-wave
amplitute, and discuss about its implications. Second, the new
mesurements
of branching ratios, BR(D+ -> K pi mu nu)/BR(D+ -> K 2pi) and BR(Ds ->
phi
mu nu)/BR(Ds -> K phi) will be shown. Lastly, the recently published
results of the form factor ratios for the K* mu nu will be discussed.

    Related papers: Phys. Lett. B535:43-51,2002 / hep-ex/0203031;
                    Phys. Lett. B541:243-250,2002 / hep-ex/0206056;
                    Phys. Lett. B544:89-96,2002 / hep-ex/0207049.