Multiplicity is one of the most fundamental observable properties of massive O-type stars and offers a promising way to discriminate between massive star formation theories .
Nevertheless , companions at separations between 1 and 100 milli-arcsec ( mas ) remain mostly unknown due to intrinsic observational limitations .
At a typical distance of 2 kpc , this corresponds to projected physical separations of 2-200 AU .
The Southern MAssive Stars at High angular resolution survey ( sm a sh + ) was designed to fill this gap by providing the first systematic interferometric survey of Galactic massive stars .
We observed 117 O-type stars with VLTI/PIONIER and 162 O-type stars with NACO/SAM , respectively probing the separation ranges 1-45 and 30-250 mas and brightness contrasts of \Delta H < 4 and \Delta H < 5 .
Taking advantage of NACO ’ s field-of-view , we further uniformly searched for visual companions in an 8″-radius down to \Delta H = 8 .
This paper describes the observations and data analysis , reports the discovery of almost 200 new companions in the separation range from 1 mas to 8″ and presents the catalog of detections , including the first resolved measurements of over a dozen known long-period spectroscopic binaries .

Excluding known runaway stars for which no companions are detected , 96 objects in our main sample ( \delta < 0 ° ; H < 7.5 ) were observed both with PIONIER and NACO/SAM .
The fraction of these stars with at least one resolved companion within 200 mas is 0.53 .
Accounting for known but unresolved spectroscopic or eclipsing companions , the multiplicity fraction at separation \rho < 8 ″ increases to f _ { \mathrm { m } } = 0.91 \pm 0.03 .
The fraction of luminosity class V stars that have a bound companion reaches 100 % at 30 mas while their average number of physically connected companions within 8″ is f _ { \mathrm { c } } = 2.2 \pm 0.3 .
This demonstrates that massive stars form nearly exclusively in multiple systems .
The nine non-thermal radio emitters observed by sm a sh + are all resolved , including the newly discovered pairs HD 168112 and CPD - 47°2963 .
This lends strong support to the universality of the wind-wind collision scenario to explain the non-thermal emission from O-type stars .