As well as trade issues, Mrs Clinton will also speak up for women's rights
US Secretary of State Hillary Clinton has begun her 11-day tour of the Africa saying improving democracy is the key to boosting trade and development.
She told a summit in Kenya investors would not be attracted to states with failed leadership and civil unrest.
Later she will meet Kenyan leaders, amid growing concerns over Nairobi's reluctance to seek justice following last year's post-election violence.
During her seven-nation tour, she is also expected to hold talks on Somalia.
Analysts say the tour, her longest overseas journey in her post to date, is part of an attempt by the US to show that Africa remains a key foreign policy priority.
Her trip comes less than a month after US President Barack Obama, whose father was born in Kenya, travelled to Ghana.
Mr Obama said in a video broadcast to delegates at the Nairobi summit that he would like to see closer trade ties with Africa.
US officials were keen to emphasise that Mrs Clinton's trip is the earliest trip by a secretary of state to Africa of any administration.
One of Mrs Clinton's first engagements in Nairobi was to address a forum of some 40 African states which enjoy trade preferences with the US - through the Africa Growth and Opportunity Act (Agoa) - on the condition they uphold free elections and markets.
ANALYSIS: US-AFRICAN TRADE
Martin Plaut, BBC News
Since it was initiated in 2000, the Africa Growth and Opportunity Act (Agoa) has done wonders for trade between America and Africa. Its proponents point to its successes: a 300% increase in trade and the creation of 300,000 African jobs.
But sceptics are more cautious. About 80% of all African exports come in the form of oil - something the US was never going to do without. And most of the non-oil exports come from a handful of southern African nations, which have boosted their clothing and textile trade with America.
Even these gains are now under threat. There is a plan before the Obama administration to expand the preferential trade terms in Agoa to other developing states. This is being fiercely resisted by Washington's vocal African-American lobby.
This issue is critical, but so too is the question of American subsidies to its farmers. It undercuts African farmers, making it impossible for them to compete in international markets. But here the US has so far dug in its heels.
She said Africa had all the ingredients for growth, prosperity and progress and should reject corruption.
"The solution starts with transparency. A famous judge in my country once said that sunlight is the best disinfectant. And there's a lot of sunlight in Africa," she said.
"We can't seem to get past the idea that the continent has enormous potential for progress.
"Too often the media's portrayal is so much less than that. But such notions are not only stale and outdated - they are wrong."
The greatest opportunity for Africa lay in boosting trade within the continent, she said.
Mrs Clinton ended by shining the spotlight on Africa's women saying they had often been marginalised but were key to transforming economies.
She will hold talks with Kenyan President Mwai Kibaki and Prime Minister Raila Odinga later.
Before Mrs Clinton arrived in Kenya, the US embassy in Nairobi issued a statement scolding Kenya for its decision not to set up a local court to seek justice for the victims of the country's post-poll clashes.
Democratic Republic of Congo
At least 1,300 people died during clashes following the disputed December 2007 election.
"The US is deeply concerned by the coalition government's decision that appears to indicate it will not pursue establishment of an independent Special Tribunal to hold accountable perpetrators of post-election violence," the US government said in the statement.
Meanwhile, Somali President Sheik Sharif Sheik Ahmed said his planned meeting with Mrs Clinton in Kenya would be "a golden chance for the Somali people and government".
"It signals how the American government, the Obama administration and the international community are willing to support Somalia this time," he said, referring to earlier failed peacekeeping missions to the country.
Mrs Clinton will also visit South Africa, Nigeria, Angola, Liberia, the Democratic Republic of Congo and Cape Verde.