Atomically precise triple step staircase with a periodicity of about 6 nm can be fabricated on clean Si(557) surface using special sample treatment under ultra-high vacuum . This semiconducting template is very promising for fabrication of low dimensional (1D, 2D) metallic and molecular structures with unique physical properties. However, despite numerous studies of metal/Si(557) systems, the precise atomic structure of clean Si(557) surface is still controversial [1-4]. The results of previous studies suggest that it can be related to the formation of different step arrays with different local surface orientations, i.e. Si(557) [1-3], Si(7 7 10) , Si(223) [5,6]. Here we report high resolution STM and LEED studies of well-ordered step array fabricated on a Si(557) sample with a miscut of 9.5° from the (111) plane using special annealing procedure with electric current directed perpendicular to the steps. The STM data show that after precise sample preparation the triple step array is extremely uniform: On some micrometer-scale surface areas the number of periodicity breakings can be as low as one per more than one hundred hill and valley sequences. According to our LEED and atomically resolved STM data the periodicity of this regular grating on the vicinal silicon surface is 5.9±0.2 nm that is most close to the Si(557) surface orientation. STM studies show that despite the high uniformity of the fabricated grating, there are at least four possible step and terrace configurations maintaining exactly the same groove periodicity throughout the surface. The atomic structure of the staircase and sample preparation strategy for fabrication of high quality step array and different nanostructures on the Si(557) surface are discussed.