Keep two questions apart, because almost every confused discussion of this topic merges them. Whether a system is intelligent concerns what it can do, and is testable. Whether it is conscious concerns whether there is anything it is like to be it, and no known test touches that directly. A system might be highly intelligent with nothing inside, or — less intuitively — have experiences it cannot report.
The difficulty is structural rather than technological. Consider how you conclude other people are conscious. You observe behaviour resembling yours, and you know they are physically constituted much as you are. Neither alone would carry much weight; together they support a strong inference. A machine breaks this pair: it may match the behaviour arbitrarily well while sharing none of the physical constitution. The inference we rely on for every other case simply does not apply, and we have no replacement for it.
What you conclude therefore depends on which theory of consciousness you hold — and the theories disagree sharply. Functionalism holds that mental states are defined by their causal roles, so any system implementing the right organisation is conscious regardless of material; on this view machine consciousness is possible in principle and perhaps already a matter of degree. Biological naturalism, Searle's position, holds that consciousness arises from the specific causal powers of brains, so silicon implementing the same abstract pattern would not qualify. Integrated information theory ties consciousness to a measurable property of a system's causal structure, which would make some architectures conscious and others not, largely independently of how intelligently they behave. Illusionism denies there is a further fact to establish at all.
Notice that these disagree about actual systems, not just hypothetical ones, and that no experiment currently distinguishes between them. That is the real situation: not that the answer is unknown pending more research, but that we do not have an agreed method by which research would produce the answer.
The practical upshot deserves stating plainly. We may build systems whose moral status is genuinely uncertain, and uncertainty will not excuse us from acting. There is also a distorting factor worth naming — we are strongly disposed to attribute minds to things that use language well, which means our intuitions here are unusually unreliable in exactly the cases that matter most. Fluency is evidence of fluency. Whether it is evidence of anything further is precisely the question, and treating the first as settling the second is the mistake this whole area is designed to expose.