Monodisperse FePt nanoparticles with an average particle size of 2.7 nm are synthesized by a polyol process and an etched silicon structure is also formed by an electrochemical process in HF acid. Then, the etched silicon surface as a substrate is coated with FePt nanoparticles. Chemical bonding between nanoparticles and the etched silicon surface prevents the coalescence of the particles during thermal annealing. Annealing at 600 degrees C for 1 h under a reducing atmosphere (90Ar% + 10H(2)%) leads to realize phase transformation from fcc to fct L1(0) structure and the magnetic behavior changes from the superparamagnetic into the ferromagnetic one. After annealing, the coercivity reaches a maximum value of 3.3 kOe for particles coated on the etched wafer. Furthermore, the monosize nanoparticles with an average size of 15 nm are distributed uniformly on the etched silicon surface. So, after phase transition to L10, the FePt nanoparticle size limits to the average value (15 nm). (C) 2012 Elsevier B.V. All rights reserved.