Context :

Aims : HETE J1900.1–2455 is the seventh known X-ray transient accreting millisecond pulsar and has been in outburst for more than one year .
We compared the data on HETE J1900.1–2455 with other similar objects and made an attempt at deriving constraints on the physical processes responsible for a spectral formation .

Methods : The broad-band spectrum of the persistent emission in the 2–300 keV energy band and the timing properties were studied using simultaneous INTEGRAL and publicly available RXTE data obtained in October 2005 .
The properties of the X-ray bursts observed from HETE J1900.1–2455 were also investigated .

Results : The spectrum is well described by a two-component model consisting of a blackbody-like soft X-ray emission at 0.8 keV temperature and a thermal Comptonized spectrum with electron temperature of 30 keV and Thomson optical depth \tau _ { T } \sim 2 for the slab geometry .
The source is detected by INTEGRAL up to 200 keV at a luminosity of 5 \times 10 ^ { 36 } erg s ^ { -1 } ( assuming a distance of 5 kpc ) in the 0.1–200 keV energy band .
We have also detected one type I X-ray burst which shows photospheric radius expansion .
The burst occurred at an inferred persistent emission level of \sim 3–4 % of the Eddington luminosity .
Using data for all X-ray bursts observed to date from HETE J1900.1–2455 , the burst recurrence time is estimated to be about 2 days .
No pulsations have been detected either in the RXTE or in the INTEGRAL data which puts interesting constraints on theories of magnetic field evolution in neutron star low-mass X-ray binaries .

Conclusions :